What then? Israel failed to obtain what it was seeking. The elect obtained it, but the rest were hardened,
Romans 11:7 ESV

When Paul says that the rest were hardened, this doesn’t mean that they were destined to condemnation from before birth and that God hardened their hearts so that they could never come to faith. If faith is purely a gift of God bestowed at his whim--it isn’t--then no hardening is necessary to prevent it. Those who were hardened were hardened in response to their rebellion, like Pharaoh, not to cause their rebellion.